- Email: [email protected]
butadiene rubber composites
Accepted Manuscript The role of carbon nanotubes in promoting the properties of carbon black-filled natural rubber/butadiene rubber composites Yan He, Jiangshan Gao, Xiubin Gong, Jin Xu PII: DOI: Reference:
S2211-3797(17)31439-0 https://doi.org/10.1016/j.rinp.2017.09.044 RINP 962
To appear in:
Results in Physics
Received Date: Revised Date: Accepted Date:
4 August 2017 19 September 2017 19 September 2017
Please cite this article as: He, Y., Gao, J., Gong, X., Xu, J., The role of carbon nanotubes in promoting the properties of carbon black-filled natural rubber/butadiene rubber composites, Results in Physics (2017), doi: https://doi.org/ 10.1016/j.rinp.2017.09.044
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
The role of carbon nanotubes in promoting the properties of carbon black-filled natural rubber/butadiene rubber composites Yan He, Jiangshan Gao, Xiubin Gong, Jin Xu College of Electromechanical Engineering, Qingdao University of Science and Technology, Qingdao 266061, China Corresponding author: Jiangshan Gao Email: [email protected] Abstract 80/20 natural rubber (NR) /butadiene rubber (BR) blends in which the carbon black (CB) was replaced partially by multi-walled carbon nanotubes (MWCNTs) according to the ratios m (CNTs) : m (decreasing amount of CB)=1: X (X was varied from 1 to 6), was prepared by blending of internal mixer and the two-roll mill at the mill opening of 0.5 mm for 10 times. SEM and TEM were used to investigate the filler networks and the good dispersion of fillers. The compounds containing 5 phr CNTs/27.5 phr CB exhibited the best abrasion resistance which was increased by 12.69% compared that without CNTs. 3D morphology images of wear surfaces and tensile fracture surfaces being similar to the layered map of the geography, which match the abrasion resistance and tensile properties, were observed by 3D measuring laser microscope. The uncured blend with 5 phr CNTs/35 phr CB showed the shortest cure time, the highest modulus and level of crosslink density. Significant improvement in mechanical properties were achieved by incorporating 5 phr CNTs and 35 phr CB, and the tear strength, 100 % and 300 % modulus of the vulcanizate were enhanced by 36.36 %, 61.29% and 31.63 % compared with the composite with 0 phr CNTs/40 phr CB, respectively. Additionally, compared with the composite without CNTs, the thermal conductivity of the composites with 5 phr CNTs/35 phr CB is increased by an average of 6.15% at three different temperatures. These considerable reinforcements resulted from the synergistic effect of CNTs and CB. Keywords: Synergistic effect, Carbon nanotubes, DIN abrasion, Mechanical properties, Thermal conductivity, 3D measuring laser microscope 1 Introduction Compared with natural rubber, butadiene rubber mainly used in tire manufacturing industry, is famous for the properties of high elasticity, good wear resistance, low thermogenesis. However, it reveals a poor wet skid resistance, low tear strength and tensile strength, and cold-flow characteristics. So it has to be used with other types of rubber and is often combined with natural rubber. Elasticity and deformability of the rubber elastomer are excellent, but the strength of the rubber itself could not satisfy with the requirements of the tire industry applications, therefore it is necessary to add reinforcing filler into it. The most classic filler in rubber is carbon black [1]. The drawbacks of CB are the polluting nature, black color and the need of high amounts (35-45phr)[2]. Many researches have been focused on the replacement of a significant amount of CB by another kind of filler, such as silica, nano-Al2O3, carbon nanotubes. And many emerging fillers appear continuously, among which CNTs as the rubber fillers possess a good reinforcing effect and performances [3-6]. CNTs were discovered by Iijima in 1991 and were called “the super fiber” due to its superior performances [7]. MWNTs are typical one-dimensional quantum nanomaterials with excellent mechanical properties. The tensile strength of MWNTs is up to 200 GPa, which is about 100 times of the tensile strength of steel, and its density is only 1/6 of the steel density [8]. In addition, the
Young's modulus of MWNTs is up to 1 TPa, and is about 5 times more than that of steel and comparable with diamond [9]. Although MWNTs have a high hardness, they show a good flexibility and can be extensively stretched. The thermal conductivity and electrical conductivity of MWNTs are fantastic and could be up to 6000 Wm-1 K-1[10] and 106 S/cm [11-13], respectively. In recent years, the improvements of CNTs and other fillers as hybrid filler systems to wear resistance, mechanical properties and the thermal conductivity of the polymer were reported continually [14-18]. It's proved that several kinds of fillers blended with each other as hybrid fillers are capable of reinforcing the polymer more, because it can make full use of each filler's advantage and exhibit a reinforcing effect that the single filler cannot reach. In the research of K. Ke et al.[19], part of CB particles plays an important role of bridging the gaps among CNTs when the amount of CNTs is not enough to form conductive pathways by themselves. String-like conductive network structures were formed by a CNT-CB-CNT block arrangement in the PVDF matrix. M. Galimberti et al. [20] reinforced the poly (1,4-cis-isoprene) matrix in mechanical behavior and electrical conductivity with CNTs and CB hybrid filler system. H-Y Li et al. [21] designed a compact hybrid filler network which were composed of graphene and CNTs in NR and increased the fracture toughness and tensile strength largely. J. S. Park et al. [22] enhanced the thermal conductivity of epoxy by three-dimensional carbon hybrid filler containing carbon blacks, CNTs and graphites. Many researchers studied various hybrid fillers to improve the performances of the polymer matrix, such as clay-CNTs [23], calcium ferrite- CNTs [24], lignin-silica [25], graphene oxide (rGO) - CNTs [26,27], tubular clay-grapheme [28], CNTs/PMN-PZT [29]. In general, one filler is replaced equivalently by another kind of filler in many hybrid fillers [25,30]. What's different in this paper is that CB is replaced partially by different ratios of CNTs. The purpose of this work is to study the reinforcement effect of CNTs to the carbon black-filled NR/BR compounds and the synergistic effect of the CNTs-CB hybrid filler. Usually, CNTs as fillers are easily agglomerate [31]. In this study, CNTs were filled in the composites after CB and passed through the rolls 10 times on the two-roll mill with the compounds to achieve a fine dispersion of CNTs in the rubber matrix (Fig. 2b). Then the rubber/CNTs/CB compounds with various CNTs/CB ratios were investigated by measuring their DIN abrasion, mechanical properties and thermal conductivity. To the best of our knowledge, there are not many scientific reports on the 3D morphology images of DIN abrasion surface and tensile fracture surface. 3D morphology images are like layered maps of geography and the surface roughness were used to characterize the abrasion resistance in this article. The synergistic effect of the CNTs-CB to the performances of the composites was reported. And the optimal CNTs/CB ratios relating to the optimal overall performances were studied. 2 Experimental 2.1 Materials MWCNTs of GT-300 with purity >96%, diameter 12~15 nm, length 3~12 µm were provided by Dazhan Nanomaterial Limited Company, which were manufactured by the way of catalytic chemical vapor deposition (CCVD). The carbon black used in this study was N234. Natural rubber was purchased from Hainan Natural Rubber Group and butadiene rubber (BR) was bought from Shuangli Chemical Limited Liability Company. All other chemicals were used as analytical grade apart from ones which are mentioned above. 2.2 Preparation of the CNTs/CB/rubber composite The formulations of CNTs/CB/NR/BR blends are given in Table 1. NR was plasticated by the
two-roll mill and standing for mixing. NR/BR were mixed by internal mixer (Haake Rheometer RM-200C) for 1 min at 80 oC with a rotor speed of 80 rpm, then additives, CB, MWCNTs were put in the internal mixer in turn. The mechanical properties with the sequence of CB being added ahead of MWCNTs performed better than that with the addition of MWCNTs before CB according to our previous work. And the blends were taken out when the temperature of materials reached 130 oC. The sulfur was added in the blends on the two-roll mill and it could make the sulfur well-dispersed. The mill was set to open at 0.5 mm and the compounds passed through the rolls 10 times in the different directions and this method could make CNTs achieve a good dispersion in rubber matrix according to our previous work. The cure characteristics were determined by vulkameter. Then the compounds were cured on the flat vulcanizing machine at 150 o C for 15 min. Tab.1 Composition of the composites/phr (parts per hundred of rubber). ratio of CNTs/( decreasing amount of CB)
The Xk
CNTs
CB
0a
0
0
40
1
5
35
1.5
5
32.5
2
5
30
2.5
5
27.5
3
5
25
3.5
5
22.5
1:4h
4
5
20
1:5
i
5
5
15
1:6
j
6
5
10
1:1
b
1:1.5c 1:2
d
1:2.5 1:3
e
f
1:3.5
g
Other ingredients: NR 80, BR 20, Silane coupling agent 1.2, ZnO 4, Stearic acid 2, Antioxidant 4020 2, Accelerator NS 1.5, Sulfur 1.2. a original formula of the tread rubber. b,c,d,e,f,g,h,i,j,k a part of carbon black was replaced by 5 phr CNTs (the addition of 5 phr CNTs was the empirical value of the previous experiments) according to certain proportion on the basis of the original formula, in which the weight ratio of CNTs loading/decrease of CB was fixed to m (CNTs) : m (decreasing amount of CB)=1: X. And the variable X was varied from 1 to 6 as shown above. 2.3 Characterizations The cure characteristics were examined by the rheometer (Gotech GT-M2000-A) at 150 ℃ for 30 min. Anti-wear performances of the composites were examined by DIN abrasion resistance tester (Gotech Testing Machines Inc., Taiwan), and repeated the test 3 times. Cylindrical samples were subjected to the vertical force of 5N and the wear stroke was 40 m. Tensile and tear properties were measured by servo controlled tensile testing machine of Gotech (GT/AI-7000M) with rising speed of 500 mm•min-1, take the medians. Morphologies of the wear surfaces and tensile fracture-surfaces were performed by 3D measuring laser microscope (OLS4100). And the surface roughness of wear surface was measured by it as well, repeat the test 3 times and take 3 areas per sample. The morphology of the quenching surfaces was observed by SEM (HITACHI
SU8000) with the accelerating voltage 5 KV. The dispersion of hybrid fillers was observed by TEM (JEM-2100) with the accelerating voltage 200 KV. Thermal conductivity of the composites was examined by Netzsch Laser Flash Analysis (LFA447). 3 Results and discussion 3.1 The cure characteristics Tab. 2 The cure characteristics of the composites Ratios(1:X)
ML/dN·m
MH/dN·m
(MH-ML)
t10/min
t90/min
0 CNTs 1:1 1:1.5 1:2 1:2.5 1:3 1:3.5 1:4 1:5 1:6
1.46 2.68 2.26 2.22 2.09 1.87 1.72 1.46 1.36 1.12
15.01 18.38 17.21 17.14 16.58 15.43 15.12 14.87 13.23 12.65
13.55 15.70 14.95 14.92 14.49 13.56 13.40 13.41 11.87 11.53
3.62 2.25 2.27 2.28 2.32 2.47 2.52 2.62 3.07 3.45
9.72 8.97 9.03 9.17 9.22 9.23 9.39 9.52 9.65 9.73
In Table 2, the minimum torque (ML), the maximum torque (MH), and the torque difference (MH-ML) of the composites are decreased with the increasing X. ML and MH mean the mobility and modulus of the uncured rubber, respectively. The mobility and modulus of the uncured rubber are reduced due to the decreased CB content. The torque difference is typically an indication of the crosslink density in a rubber composite [32,33]. The restrictions of fillers to rubber molecular chains are reduced because of the decreasing CB and crosslink density. In Table 2, it is also seen that the scorch time (t10) and cure time (t90) of the composites were significantly increased with the decreased CB content. The shortest t90 of the composite in [34] is 10.57 min and the short cure time in the present paper is energy-efficient. This is claimed that the reduced filler bring the thermal conductivity of the composites down (Fig. 7), leading to delayed onset of vulcanization [35,36]. Moreover, less frictional heat was generated with the decreased CB content in the mixing process. This increased the scorch and cure times of the rubber compounds but decreased the rate of crosslinking reactions [32]. 3.2 Abrasion performance The surface morphology of the earth can be obtained from the layered map of the geography, in which different colors represent different heights and terrains. Similarly, the surface relief of DIN abrasion can be observed by 3D measuring laser microscope and can get the 3D height map with different colors to distinguish relative heights in the viewing area. The colors' variation from red to blue indicates that the height of wear surface is from high to low in Fig. 1. Soft rubber materials abrade in a characteristic way, forming protruding ridges which are lying at right angles to the sliding direction [37]. The figure shows that the worn surface is like sea waves, the red ridges are like sprays and the blue section is a strip of depression. In Fig. 1a, the boundary among different colors is not obvious, that is, the ridge height is relatively low, and the surface roughness is 3.710 µm in Fig. 4. In Fig. 1b, the color boundary is obvious, and the surface roughness is 3.316 µm in Fig. 4. As can be seen in Fig. 1c, the chromatic aberration is the most obvious, the ridge height is the maximum, and matches the biggest surface roughness of 3.904 µm in Fig. 4. An
explanation for the differences is that different wear resistance results in different morphologies of wear surface, an evidence for this is that the abrasion volume loss of the composites with ratio 1:1, 1:2.5, 1:5 is 134 mm3, 117 mm3, and 136 mm3 in Fig. 3. Therefore, the morphology of Fig. 1 is satisfied with the results of surface roughness and the abrasion resistance.
(a) (b) (c) Fig. 1. 3D measuring laser microscope height images of DIN wear surface at 10 times magnification. (a), (b) and (c) are the composite images of the ratio 1:1, 1:2.5, 1:5, respectively. From Fig. 2(a), we can see that the both ends of CNTs are buried in the rubber matrix, it means a good interface cohesion between CNTs and the rubber matrix. As can be seen in Fig. 2(b), carbon black aggregations and CNTs have a good dispersion and can contact with each other in the rubber blends, and CNTs are like the bridges between carbon black aggregations and carbon black aggregations are like the bridges between CNTs. This matches the bridging effect in Fig. 7(a). (a)
Fig. 2. SEM image of the quenching surface and TEM image. ( (a): uncured rubber with the ratio 1:2.5, (b):cured rubber with the ratio 1:1)
155 3
147mm 1:6
3
DIN(volume abrasion loss/mm )
150 145 3
134mm 1:1 140 135 130 125
20.41% 12.69%
120 115
3
117mm 1:2.5
110 1
2
3
4
5
6
The X
Fig. 3. Effect of the CNTs/CB ratios on the DIN abrasion loss (The wear surface morphology of the wear sample with the ratio 1:1 was amplified by 50 times in the inset.) As is well known, NR/BR is widely used as the tread rubber, abrasion resistance is one of the most important properties. The volume loss is used to express the abrasion resistance of vulcanizates. The higher volume loss means the lower abrasion resistance of the vulcanizates. As shown in Fig. 3, the volume loss curve of DIN abrasion illustrates a "V" shape. The composite with ratio 1:2.5 (5 phr CNTs and 27.5 phr CB) exhibited the highest anti-wear resistance, which increased by 12.69% and 20.14% compared with the composites of the ratio 1:1 and 1:6, respectively. The improvement of abrasion resistance of the dual filler composites containing 5 phr CNTs and 27.5 phr CB is attributed to the appropriate intercalation and better filler-filler-matrix interaction [2]. The excessive fillers make the composites brittle when the ratio is 1:1, thus the abrasion resistance of composites is rised initially due to the decrease of CB loading. It has been reported that hardness, modulus of the vulcanizate play important roles on controlling the abrasion resistance [38-41]. So the abrasion resistance of composites starts to decrease when the X is more than 2.5 because of the sharp drop of modulus and hardness of the vulcanizate in Fig. 6(b) and (c).
4.3 4.2 4.1 4.0 3.9
Sa/um
3.8 3.7 3.6 3.5 3.4 3.3 3.2 1
2
3
4
5
6
The X
Fig. 4. The surface roughness (Sa) of abrasion surfaces The surface roughness of the metals has a certain impact on the fitting property, wear resistance, contact stiffness of machine parts, then it's naturally associated with the abrasion surface roughness of polymers and their wear resistances definitely possess a close relationship with each other. The roughness (Sa) of the worn surface is tested by 3D measuring laser microscope. In general, Ra is used to represent the surface roughness. However, in the research of B. K. Li [42], Sa can reflect the surface randomness of the workpiece with respect to the Ra, which can represent the micro-overall characteristics of the surface more accurately than Ra. Therefore, the arithmetic mean deviation (Sa) is used to stand for the micro-surface roughness of composites in this paper. The curve of surface roughness is similar to the curve of volume loss (Fig. 3), which exhibits a “V” shape, as seen in Fig. 4. It shows that the stronger the wear resistance is, the smaller the surface roughness is. Furthermore, the increase of the roughness value is attributed to the decrease of abrasion resistance, as shown in Fig. 1. For instance, the smallest roughness of wear surface and the tiny height difference of the composite with ratio 1:2.5 are consistent with the smallest volume loss and the best abrasion resistance. Therefore, the wear resistance of the composites can not only be expressed by the volume loss directly, but also can be characterized by 3D height maps of the abrasion surfaces and the values of roughness. 3.3 Mechanical properties of the composite
a
a’
a’’
b
b’
b’’
c c’ c’’ Fig. 5. 3D measuring laser microscope images of the tensile fracture surfaces. a, a’, a’’: CNTs/CB ratio 1:1, b, b’, b’’: CNTs/CB ratio 1:2.5, c, c’, c’’: CNTs/CB ratio 1:6. a, b, c: colorized imagesat10 times magnification, a’, b’, c’: chromograms magnified 20 times, a’’, b’’, c’’:3D height maps at the magnification of 20 times. As shown in Fig. 5a and 5a’, the tensile fracture surfaces are smooth and uniform. The height difference is low as seen in Fig 5a’’. From Fig. 5b and 5b’’, a lot of cracks and a bar-like bulge between two cracks are observed. Thick cracks and obvious grooves are presented clearly in Fig. 5c. The altitude difference is relatively high in Fig. 5c’’. In Fig. 6a, the tensile strength of Fig. 5a, Fig. 5b, Fig. 5c is 24.10MPa, 23.80 MPa, 22.06 MPa, respectively. It indicates that the extent of the damage of the tensile fracture surface and the tensile strength are closely linked. 24.5
3.5
24.10 MPa
13
24.0
3.0
23.5
9.26%
23.0
22.5
31.63 % 2.5
11
61.29% 10
2.0
9 1.5
22.06 MPa 22.0
8
0
1
2
3
The X
(a)
4
5
6
1.0 -1
0
1
2
3
The X
(b)
4
5
6
100%modulus/MPa
300% modulus/MPa
Tensile strength/MPa
12
73
1000
140.19KN/m
140
72 950
71
68
850
67 800
66
Tear strength/(KN/m)
900 69
Elongation/%
Hardness/Shore A
130
70
120
102.81KN/m 36.36%
110
100
51.21% 92.17KN/m
65 750
64 0
1
2
3
The X
4
5
6
90 0
1
2
3
4
5
6
The X
(c) (d) Fig. 6. The mechanical properties of the composites. ( a: the tensile strength, b: 100% and 300% modulus, c: hardness and elongation at break, d:the tear strength) As shown in Fig. 6, the tensile strength, modulus, and hardness of the compounds tend to decrease except for the enhancement of the elongation at break with the increase of the X, when the X is bigger than 1. The optimum results are obtained when the CNTs/CB ratio is 1:1, the tensile strength and the hardness are enhanced, and the tear strength, 100 % and 300 % modulus of the nanocomposites are increased by 36.36 %, 61.29% and 31.63 % respectively, compared with the composites without CNTs. While the filler mass of the composite without CNTs (40 phr CB) is same as the composite with CNTs/CB ratio 1:1 (5 phr CNTs/35 phr CB), CNTs are tough filler relatively (the young's modulus of CNTs is 1TPa in theory [7]). In addition, the higher aspect ratio of CNTs, which is around 500 times compared with CB [30], more physical or chemical contacts between CNTs and the rubber matrix can reinforce the polymer matrix, which can carry more imposed stress to avoid damage to the polymer chains when the matrix is under load. The tensile strength and tear strength are higher than the composites in [43]. When the X is more than 1, the mechanical properties are reduced because of the decrease of carbon black. Meanwhile, a rise in elongation at break (Fig. 6c) is observed because the limitation of the filler networks to the movement of the polymer chains and the crosslink density (Table 2) are reduced. The tensile strength results are agree with the tensile fracture surfaces from Fig. 5. 3.4 Thermal conductivity
(b)
0.29
-1
Thermal conductivity/Wm K
-1
0.28 0.27 0.26 0.25
(a) 0.24 0.23
o
80 C o 100 C o 120 C
0.22 0.21 0
1
2
3
4
5
6
The X
Fig. 7. The thermal conductivity of the compounds and Schematic diagram of the network structure consisting of CNTs and CB [19,44,45] As shown in Fig. 7, the thermal conductivity of the compounds is increased with the rise of the temperature. Because the rise of the temperature can stimulate a more high-frequency phonon which is the medium of conveying heat in rubber composites. What is more, the curves of the thermal conductivity show the decrease trend when the X is more than 1, the thermal conductivity of the composites with CNTs/CB ratio 1:1 is increased by an average of 6.15% at three temperatures than the composites without CNTs. While the formula of composites with CNTs/CB ratio 1:1 is equal to 5 phr CB replaced by 5 phr CNTs compared with the composites without CNTs. It's attributed to that CNTs are one of the most powerful materials in thermal conductivity (the theoretical thermal conductivity is up to 6000 Wm-1K-1 along the axial of a single carbon nanotube [9] and the thermal conductivity of CB is 6~174 Wm-1 K-1 at 25 oC [46] ).In addition, the higher aspect ratio of CNTs, which is around 500 times compared with CB, is conducive to make CNTs contact with each other to enhance the thermal conductivity. Afterwards, the thermal conductivity is decreased when the X is more than 1. This result is believed to be associated with the bridge effect of physical contracts between CB particles and CNTs (Fig. 2(b)), the vibrations of phonon can flow more efficiently through the paths of interconnected CB particles and CNTs when the ratio is 1: 1 in Fig. 7(a) [19,44,45,47] and the bridge effect is waken with the reduction of CB loading in Fig. 7(b). Conclusions It can be concluded that CNTs and CB as a hybrid filler could create much stronger filler networks. Partial replacements of CB with different ratios of CNTs could enhance the abrasion resistance due to the synergistic effect. The compounds containing 5 phr CNTs and 27.5 phr of CB in hybrid filler show the optimal abrasion resistance and the smallest surface roughness (Sa). The vulcanizate with the CNTs/CB ratio 1:1 demonstrates the optimum overall mechanical properties, the cure characteristics and thermal conductivity, which makes it promise the tire tread with a long service life, short cure time and high thermal conductivity. The CB bridging effect could make the perfect thermal networks and a sufficient amount of
CB is required for high thermal conductivity. The ridges and cracks of the wear surface and tensile fracture surface in 3D images can exhibit the degree of wear and the tensile strength to some extent and this is a visualized access to characterize the composites. Acknowledgements This work was supported by the National Natural Science Foundation of China (No. 51676103 and 51276091).
References [1] N. Rattanasom, T. Saowapark, C. Deeprasertkul, Reinforcement of natural rubber with silica/carbon black hybrid filler, Polym. Test. 26 (2007) 369-377. [2] S.A. Shooli, M. Tavakoli. Styrene Butadiene Rubber/Epoxidized Natural Rubber (SBR/ENR50) Nanocomposites Containing Nanoclay and Carbon Black as Fillers for Application in Tire-Tread Compounds. J. Macromol. Sci. B, 2016. [3] A. D. Falco, S. Goyanes, G. H. Rubiolo, I. Mondragon, A. Marzocca, Carbon nanotubes as reinforcement of styrene-butadiene rubber, Appl. Surf. Sci. 254 (2007) 262-265. [4] A. Fakhru’l-Razi, M. A. Atieh, N. Girun, T. G. Chuah, M. El-Sadig, D. R. A. Biak, Effect of multi-wall carbon nanotubes on the mechanical properties of natural rubber, Compos. Struct. 75 (2001) 496-500. [5] A.M. Vorobei, O. I. Pokrovskiy, K. B. Ustinovich, Preparation of polymer multi-walled carbon nanotube composites with enhanced mechanical properties using supercritical antisolvent precipitation, Polymer 95 (2016) 77-81. [6] Y. He, Z. -F. Cao, L. -X. Ma, Shear Flow Induced Alignment of Carbon Nanotubes in Natural Rubber, Int. J. Polym. Sci. 2015 (2015). [7] S. Iijima, Helical microtubes of graphitic carbon, Nature 354 (1991) 56-58. [8] J. Park, K. H. Lee, Carbon nanotube yarns, Korean J. Chem. Eng. 29 (2012) 277-287. [9] H. Shima, Buckling of carbon nanotubes: a state of the art review, Materials 5 (2011) 47-84. [10] B. Zhou, W. Luo, J.-Q. Yang, X.-B. Duan, Y. -W. Wen, H. -M. Zhou, R. Chen, B. Shan, Thermal conductivity of aligned CNT/polymer composites using mesoscopic simulation, Compos: Part A-Appl. S. 90 (2016) 410-416. [11] J.-Y. Wang, H. -B. Jia, L. -F. Ding, L. -J. Zhu, X. Dai, X. Fei, F. Li, X. -D. Gong. Utilization of silane functionalized carbon nanotubes-silica hybrids as novel reinforcing fillers for solution styrene butadiene rubber, Polym. Compos. 34 (2013) 690-696. [12] S. Berber, Y. K. Kwon, D. Tomanek, Unusually high thermal conductivity of carbon nanotubes, Phys. Rev. Lett. 84 (2000) 4613-4616. [13] T. W. Ebbesen, H. J. Lezec, H. Hiura, J. W. Bennett, H. F. Ghaemi, T. Thio, Electrical conductivity of individual carbon nanotubes, Nature, 382 (1996) 54-56. [14] X. -J. Zhang, P. -Y. Dong, Y. Chen, W. -C. Yang, Y. -Z. Zhan, K. -F. Wu, Y.-Y. Chao, Fabrication and tribological properties of copper matrix composite with short carbon fiber/ reduced graphene oxide filler, Trib. Int. 103 (2016) 406-411. [15] K. Wu, C. -X. Lei, W. -X. Yang, S. -G. Chai, F. Chen, Q. Fu, Surface modification of boron nitride by reduced graphene oxide for preparation of dielectric material with enhanced dielectric constant and well-suppressed dielectric loss, Compos. Sci. Technol. 134 (2016) 191-200. [16] W. -H. Yuan, Q. -Q. Xiao, L. Li, T. Xu, Thermal conductivity of epoxy adhesive enhanced by hybrid graphene oxide/AIN particles, Appl. Therm. Eng. 103 (2016) 1067-1074. [17] J. Bastos- Arrieta, J. Muñoz, A. Stenbock-Fermor, M. Muñoz, D.N. Muraviev, F. Céspedes, L.
A. Tsarkova, M. Baeza, Intermatrix synthesis as a rapid, inexpensive and reproducible methodology for the in situ functionalization of nanostructured surfaces with quantum dots, Appl. Surf. Sci. 368 (2016) 417-426. [18] A. Das, G.R. Kasaliwal, R. Jurk, R. Boldt, D. Fischer, K.W. Stockelhuber, G. Heinrich, Rubber composites based on grapheme nanoplatelets, expanded graphite, carbon nanotubes and their combination: a comparative study, Compos. Sci. Technol. 72 (2012) 1961-1967. [19] K. Ke, P. Pötschke, N. Wiegand, B. Krause, B. Voit, Tuning the network structure in poly (vinylidene fluoride)/carbon nanotube nanocomposites using carbon black: toward improvements of conductivity and piezoresistive sensitivity, Acs. Appl. Mater. Inter. 8 (2016) 14190-14199. [20] M. Galimberti, M. Coombs, P. Riccio, T. Ricco`, S. Passera, S. Pandini, L. Conzatti, A. Ravasio, I. Tritto, The role of CNTs in promoting hybrid filler networking and synergism with carbon black in the mechanical behavior of filled polyisoprene, Macromol. Mater. Eng. 298 (2013) 241-251. [21] H. -Y. Li, L. Yang, G. -S. Weng, Toughening rubbers with a hybrid filler network of graphene and carbon nanotubes, J. Mater. Chem. A. 3 (2015), 22385-22392. [22] J. -I. Sun Park, J. -A. You, K. Shin, J. -H. Han, C. -S. Lee, Enhanced thermal conductivity of epoxy/three-dimensional carbon hybrid filler composites for effective heat dissipation, RSC Adv. 5 (2015) 46989-46996. [23] G. Gorrasi, S. D’Ambrosio, G. Patimo, R. Pantani, Hybrid clay-carbon nanotube/PET composites: preparation, processing, and analysis of physical properties, J. Appl. Polym. Sci. 131 (2014) 40441-40448. [24] G. Gorrasi, C. Milone, E. Piperopoulos, R. Pantani, Preparation, processing and analysis of physical properties of calcium ferrite-CNTs/PET nano-composite, Compos. Part B-Eng. 81 (2015) 44-52. [25] P. Yu, H. He, Y. -C. Jia, S. -H. Tian, J. Chen, D. Jia, Y. -F. Luo, A comprehensive study on lignin as a green alternative of silica in natural rubber composites, Polym. Test. 54 (2016) 176-185. [26] S. Wu, L. -Q. Zhang, P. -J. Weng, Z.-J. Yang, Z. -H. Tang, B. -C. Guo, Correlating synergistic reinforcement with chain motion in elastomer/nanocarbon hybrids composites, Soft Matter. 12 (2016) 6893-6901. [27] J.-K. Wu , C.-C. Ye , T. Liu , Q.-F. An , Y.-H. Song , K.-R. Lee ,W.-S. Hung , C.-J. Gao, Synergistic effects of CNT and GO on enhancing mechanical properties and separation performance of polyelectrolyte complex membranes, Mater. Design 119 (2017) 38-46. [28] Z. Tang, Q. Wei, T. Lin, B. Guo, D. Jia, The use of a hybrid consisting of tubular clay and graphene as a reinforcement for elastomers, RSC Adv. 3 (2013) 17057-17064. [29] M. Ma, X. Wang, Preparation, microstructure and properties of epoxy-based composites containing carbon nanotubes and PMN-PZT piezoceramics as rigid piezo-damping materials. Mater. Chem. Phys. 116(2009) 191-197. [30] M. Poikelispää, A. Das, W. Dierkes, V. Jyrki, The effect of partial replacement of carbon black by carbon nanotubes on the properties of natural rubber/butadiene rubber compound, J. Appl. Polym. Sci. 130 (2014) 3153-3160. [31] S. M. Park, Y. W. Lim, C. H. Kim, D. J. Kim, W.-J. Moon, J. -H. Kim, J. -S. Lee, C. K. Hong, G. Seo, Effect of carbon nanotubes with different lengths on mechanical and electrical properties of silica-filled styrene butadiene rubber compounds, J. Ind. Eng. Chem. 19 (2013) 712-719.
[32] S. Matchawet, A. Kaesaman, P. Bomlai, C. Nakason. Effects of multi-walled carbon nanotubes and conductive carbon black on electrical, dielectric, and mechanical properties of epoxidized natural rubber composites. Polym. Composite., 38(2015) 1031-1042. [33] H. Ismail and B.T. Poh. Cure and tear properties of ENR 25/SMR L and ENR 50/SMR L blends. Eur. Polym. J., 36 (2000) 2403-2408 [34] D. F. Castro, J. C. M. Suarez, R. C. R. Nunes, L.L.Y. Visconte. Influence of mixing procedures and mica addition on properties of NR/BR vulcanizates. I. J. Appl. Poly. Sci., 94(2010) 1575-1585. [35] M.A. L opez-Manchado, J. Biagiotti, L. Valentini, and J.M. Kenny, Dynamic mechanical and Raman spectroscopy studies on interaction between single-walled carbon nanotubes and natural rubber. J. Appl. Polym. Sci., 92 (2004) 3394-3400. [36] G. Sui, W. Zhong, X. Yang, and S. Zhao, Processing and Material Characteristics of a Carbon ‐Nanotube‐Reinforced Natural Rubber. Macromol. Mater. Eng. 292 (2010) 1020-1026. [37] Y. S. Kim, S. D. Yoon, J. S. Kim, Abrasion by a blade scraper compared with abrasion by a rough surface, Polym. Test. 37 (2014) 123-128. [38] P. Yu, H. He, Y. Jia, S. Tian, J. Chen, D. Jia, Y. Luo, A comprehensive study on lignin as a green alternative of silica in natural rubber composites, Polym. Test. 54 (2016) 176-185. [39] N. Rattanasom, A. Poonsuk, T. Makmoon, Effect of curing system on the mechanical properties and heat aging resistance of natural rubber/tire tread reclaimed rubber blends, Polym. Test. 24 (2005) 728-732. [40] K. Cho, D. Lee, Effect of molecular weight between cross-links on the abrasion behavior of rubber by a blade abrader, Polymer, 41 (2001) 133-140. [41] Y. Fukahori, H. Yamazaki, Mechanism of rubber abrasion. Part I: Abrasion pattern formation in natural rubber vulcanizate, Wear, 171 (1994) 195-202. [42] B.-K. Li, Study on rule of 3D roughness average and root mean square, Tool Eng. 42 (2008) 107-110. [43] K. Pal, R. Rajasekar, J. K. Dong, X.Z. Zhen, S.K. Pal. Effect of Filler and Urethane Rubber on NR/BR with Nanosilica: Morphology and Wear. J. Thermoplast. Compos., 23(2010) 717-739. [44] T. W. Lee, H. H. Park, The effect of MWCNTs on the electrical properties of a stretchable carbon composite electrode, Compos. Sci. Technol. 114 (2015) 11-16. [45] K. Yu, Z.-C. Zhang, Y.-J. Liu, and J.-S. Leng, Carbon nanotube chains in a shape memory polymer/carbon black composite: To significantly reduce the electrical resistivity, Appl. Phys. Lett. 98(2011) 074102 [46] Z. Han, A. Fin, Thermal conductivity of carbon nanotubes and their polymer nanocomposites: A review, Prog. Polym. Sci. 36(2011) 914-944. [47] Y. G. Jeong, J. E. An, Effects of mixed carbon filler composition on electric heating behavior of thermally-cured epoxy-based composite films, Compos. Part A-Appl. 56 (2014) 1-7.
S2211-3797(17)31439-0 https://doi.org/10.1016/j.rinp.2017.09.044 RINP 962
To appear in:
Results in Physics
Received Date: Revised Date: Accepted Date:
4 August 2017 19 September 2017 19 September 2017
Please cite this article as: He, Y., Gao, J., Gong, X., Xu, J., The role of carbon nanotubes in promoting the properties of carbon black-filled natural rubber/butadiene rubber composites, Results in Physics (2017), doi: https://doi.org/ 10.1016/j.rinp.2017.09.044
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
The role of carbon nanotubes in promoting the properties of carbon black-filled natural rubber/butadiene rubber composites Yan He, Jiangshan Gao, Xiubin Gong, Jin Xu College of Electromechanical Engineering, Qingdao University of Science and Technology, Qingdao 266061, China Corresponding author: Jiangshan Gao Email: [email protected] Abstract 80/20 natural rubber (NR) /butadiene rubber (BR) blends in which the carbon black (CB) was replaced partially by multi-walled carbon nanotubes (MWCNTs) according to the ratios m (CNTs) : m (decreasing amount of CB)=1: X (X was varied from 1 to 6), was prepared by blending of internal mixer and the two-roll mill at the mill opening of 0.5 mm for 10 times. SEM and TEM were used to investigate the filler networks and the good dispersion of fillers. The compounds containing 5 phr CNTs/27.5 phr CB exhibited the best abrasion resistance which was increased by 12.69% compared that without CNTs. 3D morphology images of wear surfaces and tensile fracture surfaces being similar to the layered map of the geography, which match the abrasion resistance and tensile properties, were observed by 3D measuring laser microscope. The uncured blend with 5 phr CNTs/35 phr CB showed the shortest cure time, the highest modulus and level of crosslink density. Significant improvement in mechanical properties were achieved by incorporating 5 phr CNTs and 35 phr CB, and the tear strength, 100 % and 300 % modulus of the vulcanizate were enhanced by 36.36 %, 61.29% and 31.63 % compared with the composite with 0 phr CNTs/40 phr CB, respectively. Additionally, compared with the composite without CNTs, the thermal conductivity of the composites with 5 phr CNTs/35 phr CB is increased by an average of 6.15% at three different temperatures. These considerable reinforcements resulted from the synergistic effect of CNTs and CB. Keywords: Synergistic effect, Carbon nanotubes, DIN abrasion, Mechanical properties, Thermal conductivity, 3D measuring laser microscope 1 Introduction Compared with natural rubber, butadiene rubber mainly used in tire manufacturing industry, is famous for the properties of high elasticity, good wear resistance, low thermogenesis. However, it reveals a poor wet skid resistance, low tear strength and tensile strength, and cold-flow characteristics. So it has to be used with other types of rubber and is often combined with natural rubber. Elasticity and deformability of the rubber elastomer are excellent, but the strength of the rubber itself could not satisfy with the requirements of the tire industry applications, therefore it is necessary to add reinforcing filler into it. The most classic filler in rubber is carbon black [1]. The drawbacks of CB are the polluting nature, black color and the need of high amounts (35-45phr)[2]. Many researches have been focused on the replacement of a significant amount of CB by another kind of filler, such as silica, nano-Al2O3, carbon nanotubes. And many emerging fillers appear continuously, among which CNTs as the rubber fillers possess a good reinforcing effect and performances [3-6]. CNTs were discovered by Iijima in 1991 and were called “the super fiber” due to its superior performances [7]. MWNTs are typical one-dimensional quantum nanomaterials with excellent mechanical properties. The tensile strength of MWNTs is up to 200 GPa, which is about 100 times of the tensile strength of steel, and its density is only 1/6 of the steel density [8]. In addition, the
Young's modulus of MWNTs is up to 1 TPa, and is about 5 times more than that of steel and comparable with diamond [9]. Although MWNTs have a high hardness, they show a good flexibility and can be extensively stretched. The thermal conductivity and electrical conductivity of MWNTs are fantastic and could be up to 6000 Wm-1 K-1[10] and 106 S/cm [11-13], respectively. In recent years, the improvements of CNTs and other fillers as hybrid filler systems to wear resistance, mechanical properties and the thermal conductivity of the polymer were reported continually [14-18]. It's proved that several kinds of fillers blended with each other as hybrid fillers are capable of reinforcing the polymer more, because it can make full use of each filler's advantage and exhibit a reinforcing effect that the single filler cannot reach. In the research of K. Ke et al.[19], part of CB particles plays an important role of bridging the gaps among CNTs when the amount of CNTs is not enough to form conductive pathways by themselves. String-like conductive network structures were formed by a CNT-CB-CNT block arrangement in the PVDF matrix. M. Galimberti et al. [20] reinforced the poly (1,4-cis-isoprene) matrix in mechanical behavior and electrical conductivity with CNTs and CB hybrid filler system. H-Y Li et al. [21] designed a compact hybrid filler network which were composed of graphene and CNTs in NR and increased the fracture toughness and tensile strength largely. J. S. Park et al. [22] enhanced the thermal conductivity of epoxy by three-dimensional carbon hybrid filler containing carbon blacks, CNTs and graphites. Many researchers studied various hybrid fillers to improve the performances of the polymer matrix, such as clay-CNTs [23], calcium ferrite- CNTs [24], lignin-silica [25], graphene oxide (rGO) - CNTs [26,27], tubular clay-grapheme [28], CNTs/PMN-PZT [29]. In general, one filler is replaced equivalently by another kind of filler in many hybrid fillers [25,30]. What's different in this paper is that CB is replaced partially by different ratios of CNTs. The purpose of this work is to study the reinforcement effect of CNTs to the carbon black-filled NR/BR compounds and the synergistic effect of the CNTs-CB hybrid filler. Usually, CNTs as fillers are easily agglomerate [31]. In this study, CNTs were filled in the composites after CB and passed through the rolls 10 times on the two-roll mill with the compounds to achieve a fine dispersion of CNTs in the rubber matrix (Fig. 2b). Then the rubber/CNTs/CB compounds with various CNTs/CB ratios were investigated by measuring their DIN abrasion, mechanical properties and thermal conductivity. To the best of our knowledge, there are not many scientific reports on the 3D morphology images of DIN abrasion surface and tensile fracture surface. 3D morphology images are like layered maps of geography and the surface roughness were used to characterize the abrasion resistance in this article. The synergistic effect of the CNTs-CB to the performances of the composites was reported. And the optimal CNTs/CB ratios relating to the optimal overall performances were studied. 2 Experimental 2.1 Materials MWCNTs of GT-300 with purity >96%, diameter 12~15 nm, length 3~12 µm were provided by Dazhan Nanomaterial Limited Company, which were manufactured by the way of catalytic chemical vapor deposition (CCVD). The carbon black used in this study was N234. Natural rubber was purchased from Hainan Natural Rubber Group and butadiene rubber (BR) was bought from Shuangli Chemical Limited Liability Company. All other chemicals were used as analytical grade apart from ones which are mentioned above. 2.2 Preparation of the CNTs/CB/rubber composite The formulations of CNTs/CB/NR/BR blends are given in Table 1. NR was plasticated by the
two-roll mill and standing for mixing. NR/BR were mixed by internal mixer (Haake Rheometer RM-200C) for 1 min at 80 oC with a rotor speed of 80 rpm, then additives, CB, MWCNTs were put in the internal mixer in turn. The mechanical properties with the sequence of CB being added ahead of MWCNTs performed better than that with the addition of MWCNTs before CB according to our previous work. And the blends were taken out when the temperature of materials reached 130 oC. The sulfur was added in the blends on the two-roll mill and it could make the sulfur well-dispersed. The mill was set to open at 0.5 mm and the compounds passed through the rolls 10 times in the different directions and this method could make CNTs achieve a good dispersion in rubber matrix according to our previous work. The cure characteristics were determined by vulkameter. Then the compounds were cured on the flat vulcanizing machine at 150 o C for 15 min. Tab.1 Composition of the composites/phr (parts per hundred of rubber). ratio of CNTs/( decreasing amount of CB)
The Xk
CNTs
CB
0a
0
0
40
1
5
35
1.5
5
32.5
2
5
30
2.5
5
27.5
3
5
25
3.5
5
22.5
1:4h
4
5
20
1:5
i
5
5
15
1:6
j
6
5
10
1:1
b
1:1.5c 1:2
d
1:2.5 1:3
e
f
1:3.5
g
Other ingredients: NR 80, BR 20, Silane coupling agent 1.2, ZnO 4, Stearic acid 2, Antioxidant 4020 2, Accelerator NS 1.5, Sulfur 1.2. a original formula of the tread rubber. b,c,d,e,f,g,h,i,j,k a part of carbon black was replaced by 5 phr CNTs (the addition of 5 phr CNTs was the empirical value of the previous experiments) according to certain proportion on the basis of the original formula, in which the weight ratio of CNTs loading/decrease of CB was fixed to m (CNTs) : m (decreasing amount of CB)=1: X. And the variable X was varied from 1 to 6 as shown above. 2.3 Characterizations The cure characteristics were examined by the rheometer (Gotech GT-M2000-A) at 150 ℃ for 30 min. Anti-wear performances of the composites were examined by DIN abrasion resistance tester (Gotech Testing Machines Inc., Taiwan), and repeated the test 3 times. Cylindrical samples were subjected to the vertical force of 5N and the wear stroke was 40 m. Tensile and tear properties were measured by servo controlled tensile testing machine of Gotech (GT/AI-7000M) with rising speed of 500 mm•min-1, take the medians. Morphologies of the wear surfaces and tensile fracture-surfaces were performed by 3D measuring laser microscope (OLS4100). And the surface roughness of wear surface was measured by it as well, repeat the test 3 times and take 3 areas per sample. The morphology of the quenching surfaces was observed by SEM (HITACHI
SU8000) with the accelerating voltage 5 KV. The dispersion of hybrid fillers was observed by TEM (JEM-2100) with the accelerating voltage 200 KV. Thermal conductivity of the composites was examined by Netzsch Laser Flash Analysis (LFA447). 3 Results and discussion 3.1 The cure characteristics Tab. 2 The cure characteristics of the composites Ratios(1:X)
ML/dN·m
MH/dN·m
(MH-ML)
t10/min
t90/min
0 CNTs 1:1 1:1.5 1:2 1:2.5 1:3 1:3.5 1:4 1:5 1:6
1.46 2.68 2.26 2.22 2.09 1.87 1.72 1.46 1.36 1.12
15.01 18.38 17.21 17.14 16.58 15.43 15.12 14.87 13.23 12.65
13.55 15.70 14.95 14.92 14.49 13.56 13.40 13.41 11.87 11.53
3.62 2.25 2.27 2.28 2.32 2.47 2.52 2.62 3.07 3.45
9.72 8.97 9.03 9.17 9.22 9.23 9.39 9.52 9.65 9.73
In Table 2, the minimum torque (ML), the maximum torque (MH), and the torque difference (MH-ML) of the composites are decreased with the increasing X. ML and MH mean the mobility and modulus of the uncured rubber, respectively. The mobility and modulus of the uncured rubber are reduced due to the decreased CB content. The torque difference is typically an indication of the crosslink density in a rubber composite [32,33]. The restrictions of fillers to rubber molecular chains are reduced because of the decreasing CB and crosslink density. In Table 2, it is also seen that the scorch time (t10) and cure time (t90) of the composites were significantly increased with the decreased CB content. The shortest t90 of the composite in [34] is 10.57 min and the short cure time in the present paper is energy-efficient. This is claimed that the reduced filler bring the thermal conductivity of the composites down (Fig. 7), leading to delayed onset of vulcanization [35,36]. Moreover, less frictional heat was generated with the decreased CB content in the mixing process. This increased the scorch and cure times of the rubber compounds but decreased the rate of crosslinking reactions [32]. 3.2 Abrasion performance The surface morphology of the earth can be obtained from the layered map of the geography, in which different colors represent different heights and terrains. Similarly, the surface relief of DIN abrasion can be observed by 3D measuring laser microscope and can get the 3D height map with different colors to distinguish relative heights in the viewing area. The colors' variation from red to blue indicates that the height of wear surface is from high to low in Fig. 1. Soft rubber materials abrade in a characteristic way, forming protruding ridges which are lying at right angles to the sliding direction [37]. The figure shows that the worn surface is like sea waves, the red ridges are like sprays and the blue section is a strip of depression. In Fig. 1a, the boundary among different colors is not obvious, that is, the ridge height is relatively low, and the surface roughness is 3.710 µm in Fig. 4. In Fig. 1b, the color boundary is obvious, and the surface roughness is 3.316 µm in Fig. 4. As can be seen in Fig. 1c, the chromatic aberration is the most obvious, the ridge height is the maximum, and matches the biggest surface roughness of 3.904 µm in Fig. 4. An
explanation for the differences is that different wear resistance results in different morphologies of wear surface, an evidence for this is that the abrasion volume loss of the composites with ratio 1:1, 1:2.5, 1:5 is 134 mm3, 117 mm3, and 136 mm3 in Fig. 3. Therefore, the morphology of Fig. 1 is satisfied with the results of surface roughness and the abrasion resistance.
(a) (b) (c) Fig. 1. 3D measuring laser microscope height images of DIN wear surface at 10 times magnification. (a), (b) and (c) are the composite images of the ratio 1:1, 1:2.5, 1:5, respectively. From Fig. 2(a), we can see that the both ends of CNTs are buried in the rubber matrix, it means a good interface cohesion between CNTs and the rubber matrix. As can be seen in Fig. 2(b), carbon black aggregations and CNTs have a good dispersion and can contact with each other in the rubber blends, and CNTs are like the bridges between carbon black aggregations and carbon black aggregations are like the bridges between CNTs. This matches the bridging effect in Fig. 7(a). (a)
Fig. 2. SEM image of the quenching surface and TEM image. ( (a): uncured rubber with the ratio 1:2.5, (b):cured rubber with the ratio 1:1)
155 3
147mm 1:6
3
DIN(volume abrasion loss/mm )
150 145 3
134mm 1:1 140 135 130 125
20.41% 12.69%
120 115
3
117mm 1:2.5
110 1
2
3
4
5
6
The X
Fig. 3. Effect of the CNTs/CB ratios on the DIN abrasion loss (The wear surface morphology of the wear sample with the ratio 1:1 was amplified by 50 times in the inset.) As is well known, NR/BR is widely used as the tread rubber, abrasion resistance is one of the most important properties. The volume loss is used to express the abrasion resistance of vulcanizates. The higher volume loss means the lower abrasion resistance of the vulcanizates. As shown in Fig. 3, the volume loss curve of DIN abrasion illustrates a "V" shape. The composite with ratio 1:2.5 (5 phr CNTs and 27.5 phr CB) exhibited the highest anti-wear resistance, which increased by 12.69% and 20.14% compared with the composites of the ratio 1:1 and 1:6, respectively. The improvement of abrasion resistance of the dual filler composites containing 5 phr CNTs and 27.5 phr CB is attributed to the appropriate intercalation and better filler-filler-matrix interaction [2]. The excessive fillers make the composites brittle when the ratio is 1:1, thus the abrasion resistance of composites is rised initially due to the decrease of CB loading. It has been reported that hardness, modulus of the vulcanizate play important roles on controlling the abrasion resistance [38-41]. So the abrasion resistance of composites starts to decrease when the X is more than 2.5 because of the sharp drop of modulus and hardness of the vulcanizate in Fig. 6(b) and (c).
4.3 4.2 4.1 4.0 3.9
Sa/um
3.8 3.7 3.6 3.5 3.4 3.3 3.2 1
2
3
4
5
6
The X
Fig. 4. The surface roughness (Sa) of abrasion surfaces The surface roughness of the metals has a certain impact on the fitting property, wear resistance, contact stiffness of machine parts, then it's naturally associated with the abrasion surface roughness of polymers and their wear resistances definitely possess a close relationship with each other. The roughness (Sa) of the worn surface is tested by 3D measuring laser microscope. In general, Ra is used to represent the surface roughness. However, in the research of B. K. Li [42], Sa can reflect the surface randomness of the workpiece with respect to the Ra, which can represent the micro-overall characteristics of the surface more accurately than Ra. Therefore, the arithmetic mean deviation (Sa) is used to stand for the micro-surface roughness of composites in this paper. The curve of surface roughness is similar to the curve of volume loss (Fig. 3), which exhibits a “V” shape, as seen in Fig. 4. It shows that the stronger the wear resistance is, the smaller the surface roughness is. Furthermore, the increase of the roughness value is attributed to the decrease of abrasion resistance, as shown in Fig. 1. For instance, the smallest roughness of wear surface and the tiny height difference of the composite with ratio 1:2.5 are consistent with the smallest volume loss and the best abrasion resistance. Therefore, the wear resistance of the composites can not only be expressed by the volume loss directly, but also can be characterized by 3D height maps of the abrasion surfaces and the values of roughness. 3.3 Mechanical properties of the composite
a
a’
a’’
b
b’
b’’
c c’ c’’ Fig. 5. 3D measuring laser microscope images of the tensile fracture surfaces. a, a’, a’’: CNTs/CB ratio 1:1, b, b’, b’’: CNTs/CB ratio 1:2.5, c, c’, c’’: CNTs/CB ratio 1:6. a, b, c: colorized imagesat10 times magnification, a’, b’, c’: chromograms magnified 20 times, a’’, b’’, c’’:3D height maps at the magnification of 20 times. As shown in Fig. 5a and 5a’, the tensile fracture surfaces are smooth and uniform. The height difference is low as seen in Fig 5a’’. From Fig. 5b and 5b’’, a lot of cracks and a bar-like bulge between two cracks are observed. Thick cracks and obvious grooves are presented clearly in Fig. 5c. The altitude difference is relatively high in Fig. 5c’’. In Fig. 6a, the tensile strength of Fig. 5a, Fig. 5b, Fig. 5c is 24.10MPa, 23.80 MPa, 22.06 MPa, respectively. It indicates that the extent of the damage of the tensile fracture surface and the tensile strength are closely linked. 24.5
3.5
24.10 MPa
13
24.0
3.0
23.5
9.26%
23.0
22.5
31.63 % 2.5
11
61.29% 10
2.0
9 1.5
22.06 MPa 22.0
8
0
1
2
3
The X
(a)
4
5
6
1.0 -1
0
1
2
3
The X
(b)
4
5
6
100%modulus/MPa
300% modulus/MPa
Tensile strength/MPa
12
73
1000
140.19KN/m
140
72 950
71
68
850
67 800
66
Tear strength/(KN/m)
900 69
Elongation/%
Hardness/Shore A
130
70
120
102.81KN/m 36.36%
110
100
51.21% 92.17KN/m
65 750
64 0
1
2
3
The X
4
5
6
90 0
1
2
3
4
5
6
The X
(c) (d) Fig. 6. The mechanical properties of the composites. ( a: the tensile strength, b: 100% and 300% modulus, c: hardness and elongation at break, d:the tear strength) As shown in Fig. 6, the tensile strength, modulus, and hardness of the compounds tend to decrease except for the enhancement of the elongation at break with the increase of the X, when the X is bigger than 1. The optimum results are obtained when the CNTs/CB ratio is 1:1, the tensile strength and the hardness are enhanced, and the tear strength, 100 % and 300 % modulus of the nanocomposites are increased by 36.36 %, 61.29% and 31.63 % respectively, compared with the composites without CNTs. While the filler mass of the composite without CNTs (40 phr CB) is same as the composite with CNTs/CB ratio 1:1 (5 phr CNTs/35 phr CB), CNTs are tough filler relatively (the young's modulus of CNTs is 1TPa in theory [7]). In addition, the higher aspect ratio of CNTs, which is around 500 times compared with CB [30], more physical or chemical contacts between CNTs and the rubber matrix can reinforce the polymer matrix, which can carry more imposed stress to avoid damage to the polymer chains when the matrix is under load. The tensile strength and tear strength are higher than the composites in [43]. When the X is more than 1, the mechanical properties are reduced because of the decrease of carbon black. Meanwhile, a rise in elongation at break (Fig. 6c) is observed because the limitation of the filler networks to the movement of the polymer chains and the crosslink density (Table 2) are reduced. The tensile strength results are agree with the tensile fracture surfaces from Fig. 5. 3.4 Thermal conductivity
(b)
0.29
-1
Thermal conductivity/Wm K
-1
0.28 0.27 0.26 0.25
(a) 0.24 0.23
o
80 C o 100 C o 120 C
0.22 0.21 0
1
2
3
4
5
6
The X
Fig. 7. The thermal conductivity of the compounds and Schematic diagram of the network structure consisting of CNTs and CB [19,44,45] As shown in Fig. 7, the thermal conductivity of the compounds is increased with the rise of the temperature. Because the rise of the temperature can stimulate a more high-frequency phonon which is the medium of conveying heat in rubber composites. What is more, the curves of the thermal conductivity show the decrease trend when the X is more than 1, the thermal conductivity of the composites with CNTs/CB ratio 1:1 is increased by an average of 6.15% at three temperatures than the composites without CNTs. While the formula of composites with CNTs/CB ratio 1:1 is equal to 5 phr CB replaced by 5 phr CNTs compared with the composites without CNTs. It's attributed to that CNTs are one of the most powerful materials in thermal conductivity (the theoretical thermal conductivity is up to 6000 Wm-1K-1 along the axial of a single carbon nanotube [9] and the thermal conductivity of CB is 6~174 Wm-1 K-1 at 25 oC [46] ).In addition, the higher aspect ratio of CNTs, which is around 500 times compared with CB, is conducive to make CNTs contact with each other to enhance the thermal conductivity. Afterwards, the thermal conductivity is decreased when the X is more than 1. This result is believed to be associated with the bridge effect of physical contracts between CB particles and CNTs (Fig. 2(b)), the vibrations of phonon can flow more efficiently through the paths of interconnected CB particles and CNTs when the ratio is 1: 1 in Fig. 7(a) [19,44,45,47] and the bridge effect is waken with the reduction of CB loading in Fig. 7(b). Conclusions It can be concluded that CNTs and CB as a hybrid filler could create much stronger filler networks. Partial replacements of CB with different ratios of CNTs could enhance the abrasion resistance due to the synergistic effect. The compounds containing 5 phr CNTs and 27.5 phr of CB in hybrid filler show the optimal abrasion resistance and the smallest surface roughness (Sa). The vulcanizate with the CNTs/CB ratio 1:1 demonstrates the optimum overall mechanical properties, the cure characteristics and thermal conductivity, which makes it promise the tire tread with a long service life, short cure time and high thermal conductivity. The CB bridging effect could make the perfect thermal networks and a sufficient amount of
CB is required for high thermal conductivity. The ridges and cracks of the wear surface and tensile fracture surface in 3D images can exhibit the degree of wear and the tensile strength to some extent and this is a visualized access to characterize the composites. Acknowledgements This work was supported by the National Natural Science Foundation of China (No. 51676103 and 51276091).
References [1] N. Rattanasom, T. Saowapark, C. Deeprasertkul, Reinforcement of natural rubber with silica/carbon black hybrid filler, Polym. Test. 26 (2007) 369-377. [2] S.A. Shooli, M. Tavakoli. Styrene Butadiene Rubber/Epoxidized Natural Rubber (SBR/ENR50) Nanocomposites Containing Nanoclay and Carbon Black as Fillers for Application in Tire-Tread Compounds. J. Macromol. Sci. B, 2016. [3] A. D. Falco, S. Goyanes, G. H. Rubiolo, I. Mondragon, A. Marzocca, Carbon nanotubes as reinforcement of styrene-butadiene rubber, Appl. Surf. Sci. 254 (2007) 262-265. [4] A. Fakhru’l-Razi, M. A. Atieh, N. Girun, T. G. Chuah, M. El-Sadig, D. R. A. Biak, Effect of multi-wall carbon nanotubes on the mechanical properties of natural rubber, Compos. Struct. 75 (2001) 496-500. [5] A.M. Vorobei, O. I. Pokrovskiy, K. B. Ustinovich, Preparation of polymer multi-walled carbon nanotube composites with enhanced mechanical properties using supercritical antisolvent precipitation, Polymer 95 (2016) 77-81. [6] Y. He, Z. -F. Cao, L. -X. Ma, Shear Flow Induced Alignment of Carbon Nanotubes in Natural Rubber, Int. J. Polym. Sci. 2015 (2015). [7] S. Iijima, Helical microtubes of graphitic carbon, Nature 354 (1991) 56-58. [8] J. Park, K. H. Lee, Carbon nanotube yarns, Korean J. Chem. Eng. 29 (2012) 277-287. [9] H. Shima, Buckling of carbon nanotubes: a state of the art review, Materials 5 (2011) 47-84. [10] B. Zhou, W. Luo, J.-Q. Yang, X.-B. Duan, Y. -W. Wen, H. -M. Zhou, R. Chen, B. Shan, Thermal conductivity of aligned CNT/polymer composites using mesoscopic simulation, Compos: Part A-Appl. S. 90 (2016) 410-416. [11] J.-Y. Wang, H. -B. Jia, L. -F. Ding, L. -J. Zhu, X. Dai, X. Fei, F. Li, X. -D. Gong. Utilization of silane functionalized carbon nanotubes-silica hybrids as novel reinforcing fillers for solution styrene butadiene rubber, Polym. Compos. 34 (2013) 690-696. [12] S. Berber, Y. K. Kwon, D. Tomanek, Unusually high thermal conductivity of carbon nanotubes, Phys. Rev. Lett. 84 (2000) 4613-4616. [13] T. W. Ebbesen, H. J. Lezec, H. Hiura, J. W. Bennett, H. F. Ghaemi, T. Thio, Electrical conductivity of individual carbon nanotubes, Nature, 382 (1996) 54-56. [14] X. -J. Zhang, P. -Y. Dong, Y. Chen, W. -C. Yang, Y. -Z. Zhan, K. -F. Wu, Y.-Y. Chao, Fabrication and tribological properties of copper matrix composite with short carbon fiber/ reduced graphene oxide filler, Trib. Int. 103 (2016) 406-411. [15] K. Wu, C. -X. Lei, W. -X. Yang, S. -G. Chai, F. Chen, Q. Fu, Surface modification of boron nitride by reduced graphene oxide for preparation of dielectric material with enhanced dielectric constant and well-suppressed dielectric loss, Compos. Sci. Technol. 134 (2016) 191-200. [16] W. -H. Yuan, Q. -Q. Xiao, L. Li, T. Xu, Thermal conductivity of epoxy adhesive enhanced by hybrid graphene oxide/AIN particles, Appl. Therm. Eng. 103 (2016) 1067-1074. [17] J. Bastos- Arrieta, J. Muñoz, A. Stenbock-Fermor, M. Muñoz, D.N. Muraviev, F. Céspedes, L.
A. Tsarkova, M. Baeza, Intermatrix synthesis as a rapid, inexpensive and reproducible methodology for the in situ functionalization of nanostructured surfaces with quantum dots, Appl. Surf. Sci. 368 (2016) 417-426. [18] A. Das, G.R. Kasaliwal, R. Jurk, R. Boldt, D. Fischer, K.W. Stockelhuber, G. Heinrich, Rubber composites based on grapheme nanoplatelets, expanded graphite, carbon nanotubes and their combination: a comparative study, Compos. Sci. Technol. 72 (2012) 1961-1967. [19] K. Ke, P. Pötschke, N. Wiegand, B. Krause, B. Voit, Tuning the network structure in poly (vinylidene fluoride)/carbon nanotube nanocomposites using carbon black: toward improvements of conductivity and piezoresistive sensitivity, Acs. Appl. Mater. Inter. 8 (2016) 14190-14199. [20] M. Galimberti, M. Coombs, P. Riccio, T. Ricco`, S. Passera, S. Pandini, L. Conzatti, A. Ravasio, I. Tritto, The role of CNTs in promoting hybrid filler networking and synergism with carbon black in the mechanical behavior of filled polyisoprene, Macromol. Mater. Eng. 298 (2013) 241-251. [21] H. -Y. Li, L. Yang, G. -S. Weng, Toughening rubbers with a hybrid filler network of graphene and carbon nanotubes, J. Mater. Chem. A. 3 (2015), 22385-22392. [22] J. -I. Sun Park, J. -A. You, K. Shin, J. -H. Han, C. -S. Lee, Enhanced thermal conductivity of epoxy/three-dimensional carbon hybrid filler composites for effective heat dissipation, RSC Adv. 5 (2015) 46989-46996. [23] G. Gorrasi, S. D’Ambrosio, G. Patimo, R. Pantani, Hybrid clay-carbon nanotube/PET composites: preparation, processing, and analysis of physical properties, J. Appl. Polym. Sci. 131 (2014) 40441-40448. [24] G. Gorrasi, C. Milone, E. Piperopoulos, R. Pantani, Preparation, processing and analysis of physical properties of calcium ferrite-CNTs/PET nano-composite, Compos. Part B-Eng. 81 (2015) 44-52. [25] P. Yu, H. He, Y. -C. Jia, S. -H. Tian, J. Chen, D. Jia, Y. -F. Luo, A comprehensive study on lignin as a green alternative of silica in natural rubber composites, Polym. Test. 54 (2016) 176-185. [26] S. Wu, L. -Q. Zhang, P. -J. Weng, Z.-J. Yang, Z. -H. Tang, B. -C. Guo, Correlating synergistic reinforcement with chain motion in elastomer/nanocarbon hybrids composites, Soft Matter. 12 (2016) 6893-6901. [27] J.-K. Wu , C.-C. Ye , T. Liu , Q.-F. An , Y.-H. Song , K.-R. Lee ,W.-S. Hung , C.-J. Gao, Synergistic effects of CNT and GO on enhancing mechanical properties and separation performance of polyelectrolyte complex membranes, Mater. Design 119 (2017) 38-46. [28] Z. Tang, Q. Wei, T. Lin, B. Guo, D. Jia, The use of a hybrid consisting of tubular clay and graphene as a reinforcement for elastomers, RSC Adv. 3 (2013) 17057-17064. [29] M. Ma, X. Wang, Preparation, microstructure and properties of epoxy-based composites containing carbon nanotubes and PMN-PZT piezoceramics as rigid piezo-damping materials. Mater. Chem. Phys. 116(2009) 191-197. [30] M. Poikelispää, A. Das, W. Dierkes, V. Jyrki, The effect of partial replacement of carbon black by carbon nanotubes on the properties of natural rubber/butadiene rubber compound, J. Appl. Polym. Sci. 130 (2014) 3153-3160. [31] S. M. Park, Y. W. Lim, C. H. Kim, D. J. Kim, W.-J. Moon, J. -H. Kim, J. -S. Lee, C. K. Hong, G. Seo, Effect of carbon nanotubes with different lengths on mechanical and electrical properties of silica-filled styrene butadiene rubber compounds, J. Ind. Eng. Chem. 19 (2013) 712-719.
[32] S. Matchawet, A. Kaesaman, P. Bomlai, C. Nakason. Effects of multi-walled carbon nanotubes and conductive carbon black on electrical, dielectric, and mechanical properties of epoxidized natural rubber composites. Polym. Composite., 38(2015) 1031-1042. [33] H. Ismail and B.T. Poh. Cure and tear properties of ENR 25/SMR L and ENR 50/SMR L blends. Eur. Polym. J., 36 (2000) 2403-2408 [34] D. F. Castro, J. C. M. Suarez, R. C. R. Nunes, L.L.Y. Visconte. Influence of mixing procedures and mica addition on properties of NR/BR vulcanizates. I. J. Appl. Poly. Sci., 94(2010) 1575-1585. [35] M.A. L opez-Manchado, J. Biagiotti, L. Valentini, and J.M. Kenny, Dynamic mechanical and Raman spectroscopy studies on interaction between single-walled carbon nanotubes and natural rubber. J. Appl. Polym. Sci., 92 (2004) 3394-3400. [36] G. Sui, W. Zhong, X. Yang, and S. Zhao, Processing and Material Characteristics of a Carbon ‐Nanotube‐Reinforced Natural Rubber. Macromol. Mater. Eng. 292 (2010) 1020-1026. [37] Y. S. Kim, S. D. Yoon, J. S. Kim, Abrasion by a blade scraper compared with abrasion by a rough surface, Polym. Test. 37 (2014) 123-128. [38] P. Yu, H. He, Y. Jia, S. Tian, J. Chen, D. Jia, Y. Luo, A comprehensive study on lignin as a green alternative of silica in natural rubber composites, Polym. Test. 54 (2016) 176-185. [39] N. Rattanasom, A. Poonsuk, T. Makmoon, Effect of curing system on the mechanical properties and heat aging resistance of natural rubber/tire tread reclaimed rubber blends, Polym. Test. 24 (2005) 728-732. [40] K. Cho, D. Lee, Effect of molecular weight between cross-links on the abrasion behavior of rubber by a blade abrader, Polymer, 41 (2001) 133-140. [41] Y. Fukahori, H. Yamazaki, Mechanism of rubber abrasion. Part I: Abrasion pattern formation in natural rubber vulcanizate, Wear, 171 (1994) 195-202. [42] B.-K. Li, Study on rule of 3D roughness average and root mean square, Tool Eng. 42 (2008) 107-110. [43] K. Pal, R. Rajasekar, J. K. Dong, X.Z. Zhen, S.K. Pal. Effect of Filler and Urethane Rubber on NR/BR with Nanosilica: Morphology and Wear. J. Thermoplast. Compos., 23(2010) 717-739. [44] T. W. Lee, H. H. Park, The effect of MWCNTs on the electrical properties of a stretchable carbon composite electrode, Compos. Sci. Technol. 114 (2015) 11-16. [45] K. Yu, Z.-C. Zhang, Y.-J. Liu, and J.-S. Leng, Carbon nanotube chains in a shape memory polymer/carbon black composite: To significantly reduce the electrical resistivity, Appl. Phys. Lett. 98(2011) 074102 [46] Z. Han, A. Fin, Thermal conductivity of carbon nanotubes and their polymer nanocomposites: A review, Prog. Polym. Sci. 36(2011) 914-944. [47] Y. G. Jeong, J. E. An, Effects of mixed carbon filler composition on electric heating behavior of thermally-cured epoxy-based composite films, Compos. Part A-Appl. 56 (2014) 1-7.